1. Field of the Invention
The present invention relates to an air conditioning apparatus for a vehicle, capable of obtaining a desired control of an engine cooling system while obtaining a desired control of the air conditioning apparatus.
2. Description of Related Art
In a vehicle provided with an internal combustion engine, a radiator located in an engine cooling water recirculating system is arranged at the front of the engine body, and a cooling fan is arranged on the rear side of the radiator. A flow of air induced not only by the movement of the vehicle but also by the rotation of the cooling fan passing through the radiator, which can improve a heat exchange occurring at the radiator. Furthermore, when the vehicle is provided with an air conditioning apparatus, a condenser for condensing the cooling medium is arranged in front of the radiator in the direction of the flow of the air. Therefore, the flow of the air first passes through the condenser, and is, then, directed to the radiator located downstream from the radiator. When the air conditioning apparatus is operating, a gas state cooling medium of high temperature, owing to the compression thereof by a compressor, is introduced into the condenser, and is subjected to a heat exchange operation with respect to the air flow, which causes the cooling medium to be condensed to a liquid. Therefore, heating of the air flow induced by the movement of the vehicle and by the rotation of the cooling fan is generated when the air flow is in contact with the condenser through which a cooling medium of high temperature is passed, and the heated air flow is directed to the radiator located downstream from the radiator in the direction of the flow of the air. At the radiator, a cooling of the recirculated engine cooling water takes place to obtain a desired temperature of the cooling medium.
It has recently been required that the air conditioning apparatus for a vehicle be much more comfortable, which necessarily increases the required cooling ability of the air conditioning apparatus for a vehicle. Furthermore, a recent preference for high power engines has resulted in an increase in the amount of heat generated from an engine. Recent requirements of luxury cars has also resulted in the increase in the number of parts in the engine compartment resulting in the existence of Very little excess space in the same. Furthermore, a declivity in of the hood is recently preferred in car design, which decreases the air generating efficiency induced by the movement of the car, resulting in a reduction in the available amount of cooling air.
When a loaded vehicle is climbing a slope in high temperatures summer it cannot be expected to obtain a high speed air flow induced by the movement of the engine, and the engine generates and emits a very large amount of heat, and the cooling demand, as required from the air conditioning apparatus, is high. In this situation, a large increase in the temperature of the air directed to the radiator portion occurs, thereby reduces the cooling ability of the cooling water in the radiator, and resulting in an increase in the temperature of the engine cooling water in the radiator.
In order to overcome the above mentioned difficulty, a solution has been proposed that stops the operation of the air conditioning apparatus when the temperature of the cooling medium exceeds a temperature of, for example, 100 degrees centigrade, or that uses a larger sized radiator or cooling fan device.
However, forced cessation of the air conditioning apparatus inevitably makes the cabin of the vehicle less comfortable. Employing a larger sized radiator fan is difficult to realize because of the limited available space in the engine compartment of the vehicle. In addition, employment of a larger sized fan does not necessarily increase the amount of air flow expected from the increase in the driving power owing to the fact that the air flow resistance of a vehicle as a total is increased.
Furthermore, when the engine is idling and therefore cannot expect to obtain an air flow caused by the movement of the vehicle, the amount of cooling air introduced into the condenser is small, thereby causing a reduction in the heat radiation efficiency of the condenser, which causes an increase in the pressure of the coolant issued from the compressor. As a result, the power necessary for driving the compressor is increased, thereby reducing the fuel consumption efficiency during the operation of the vehicle in high temperatures.